Synchro Issue?

[Beaknose]

Dear fellow NSX owners,

My '91 has an issue whenever I shift from 3rd to 4th. The car has around 76,500 miles, I do not know if the clutch is the original or a replacement. (it is an OEM). Whenever the tach is at or over 4,000 rpms, the shifter makes a unique noise that I would describe as not grinding, rather a quiet and brief squeal noise. If I shift under 4,000, the noise does not happen. When I purchased the car in June '04, the Acura tech said the clutch was weak and needed to be replaced. I have put about 4,000 miles on the car since I purchased it, the clutch feels fine and engages strong with no slipping. I do not drive the car aggressively. I never have red lined the engine, the VTEC has been engaged only a couple of times while I have owned it (I know this contradicts the real reason why we buy these cars, I guess I'm just a passive driver by nature). Therefore this squeal noise does not happen very often. The previous owner said he took the car into the dealership when he owned it to have the synchros checked, the dealership did not find anything wrong. Does anyone have any suggestions as to what might be causing this noise? Could replacing the clutch solve this issue, or is it possibly something in the gears? Thanks for all of your input and suggestions.

John
'91 Red/Ivory

 

[Lens nsx1]

I HAVE A 91 AND I HAVE HAD MY TRANS TOTALLY REBUILT BECAUSE OF THIS
PROBLEM AND GEAR WINE AND I STILL HAVE THE PROBLEM WHEN SHIFTING
FROM 3rd TO 4rth... I GUESS ITS A NORMAL CHARACTERISTIC WITH THE
NSX. FROM TALKING TO OTHER OWNERS AND BEING VERY MATICULOUS
WITH MY CAR AND EVERY LITTLE THING BOTHERING ME...

 

[Scin]

Does the car go into gear easily when you hear this noise? It may not be a synchro issue if you aren't having problems getting it into gear.

You may want to change your transmission oil, if you are having problems getting into gear you can give synchromesh friction modified a try, just search the forums for more information.

 

[Beaknose]

The answer is 'yes', it does go into gear easily whether it makes the noise or not. I didn't think about the transmission oil, thanks for the advice, I will do the search and look into it.

John
'91 Red/Ivory

 

[ScienceofSpeed]

If the noise you are discussing is a brief (about 1 second) constant pitch squeak type sound coming from the transmission area, the sound is likely the release bearing / clutch on it's way out. This usually happens when the grease has burned off and the clutch is on it's last legs. The sound may be caused by the release fork being at a sharper angle due to the worn plates.

If the sound is constant at engine speeds greater than 4k with the clutch fully engaged (I couldn't tell from your post), then the problem may be the input shaft bearing, which is usually the first bearing to go in the trans. You can test this by putting load on the trans (pressing down on the throttle while the clutch is engaged) then releasing the load (release pedal pressure). You'll hear the whiring noise change in pitch.

Cheers,
-- Chris